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The feasibility of using fiber-reinforced polymers (FRPs) as internal reinforcement for a totally reinforced concrete (RC) structure immune to corrosion essentially pertains to strength, stiffness, and deformation capacity in resisting seismic loads has become questionable. Nevertheless, no experiments have yet been conducted on the punching-shear behavior of FRP-reinforced concrete (FRPRC) slab-column connections subjected to lateral reversal cyclic loading. Consequently, current FRP-RC design guidelines and codes in North America contain no seismic provisions. This has been the main impetus to conduct the first-ever experimental study on the punching shear behavior of glass-FRP (GFRP) slab-column connections under the combination of gravity and lateral reversed cyclic loading. Four full-scale interior slab-column connections were constructed and tested to investigate the influence of flexural-reinforcement type (GFRP and steel bars), reinforcement ratio, and gravity load intensity on the punching shear performance. All test specimens were identical and measured 2500 x 2500 mm with a thickness of 200 mm. A column measuring 300 x 300 mm extended 700 mm at its center above and below the slab surfaces. The results revealed that the GFRP-RC specimens possessed adequate strength and deformation capacity against punching-shear failure during and after reserved lateral cyclic-load conditions. The GFRP-RC specimens achieved lateral interstory drift capacities over 1.50% satisfying the limits in CSA A23.3 and ACI 421.3R. The GFRP-RC specimens also had adequate drift-ductility indexes, dissipated energy, and connection stiffness. Moreover, the GFRP bar strains at the ultimate lateral-drift ratio were less than the guaranteed tensile strength by 42%. No rupture of the GFRP bars and bond failure or slip were observed during the test. [ABSTRACT FROM AUTHOR]

[Display omitted] • The stored energy evolution tends to some asymptotic value close to damage. • Analysis of the AE signal revealed two different clusters during crack propagation. • Heat dissipation correlates with AE signal cluster probably associated with crack growth. • The stored energy is sensitive to AE signal cluster probably associated with twin density. The aim of this work was to investigate the correlation between structural, acoustic emission and thermal characteristics of the fatigue crack growth in titanium alloys. Cluster analysis of the acoustic emission signals revealed two different types of signals recorded during the development of a fatigue crack. It has been shown experimentally that the evolution of the stored energy tends to an asymptotic value at the final stage of fatigue crack growth and it correlates with the intensification of the twinning process in titanium alloy Ti Grade 2. A correlation was assumed between the stages of change in the heat flux, the cumulative energy of the first cluster of AE signals and the crack length. [ABSTRACT FROM AUTHOR]

From the basic physical insight, the configuration and switching process of ferroelectric domains are both governed by energetic principles. Based on these energetic principles, a model for the nonlinear hysteretic behaviour of ferroelectric ceramics is developed. It relies on an energy-consistent thermodynamic formulation, based on two constitutive functions: free energy and dissipation. The model is grounded on an energy balance where the free energy and dissipation are known at all times during the polarisation process due to the incremental formulation obtained. All internal variables arise from the minimisation of a thermodynamic potential. Experimental measurements are performed in order to identify the parameters of the model and to validate the evolution of internal parameters generated by the energy-based model for different cases of loading. It is notably shown that the model allows capturing the energy losses under varying electrical loadings, which can be a key to the prediction of functional fatigue. • Development of an Energy-based model to describe ferroelectric hysteresis. • Choice of free energy based on a simplified multiscale model. • Dissipation defined by analogy to a mechanical dry friction force. • Multi-cell approach to characterize the different and rapidly varying strengths of pinning fields at the microscopic scale. • Comparison of polarisation and strain major loop and minor loop obtained by the model to the experimental results. [ABSTRACT FROM AUTHOR]

• Proposed a sequential test procedure for fatigue and permanent deformation damage interaction. • Proposed energy-based permanent deformation failure criterion for post-flow number deformation properties. • Strain hardening in steady state has significant effect on fatigue damage rate. • The effect pre-fatigue (less than 50% of modulus) at low temperature is marginal on deformation rate at high temperature. The dominant load-induced damages, permanent deformation (PD) and fatigue cracking (F), are traditionally predicted separately by taking temperature as a variable of departure. This paper presents an experimental study of the two damages and interaction using sequential test procedure (STP) based on 'sequential damage'. The STP is conducted in PD-F and F-PD sequences on each specimen using a creep-recovery and cyclic fatigue tests. The effect of strain hardening on fatigue cracking is studied in the PD-F sequence, and the impact of fatigue cracking on permanent deformation is explored using the F-PD sequence. First, the shear deformation in tertiary stage of creep recovery is investigated using the dissipated energy ratio criterion and a new fourth creep phase is obtained. Following the PD-F sequence, strain-hardening is found a significant accelerator of fatigue damage rate, particularly on aged and laboratory produced mixes. The fatigue tests without considering the strain-hardening effect underestimate fatigue damage rate. In the F-PD sequence, the effect of pre-existing crack (up to 40% modulus reduction) on permanent deformation is found marginal. The sequential test and damage approach is an effective way to analyze interaction between damage modes and evaluate asphalt mixtures. [ABSTRACT FROM AUTHOR]

• The dynamic tensile properties of geopolymer-concrete composites were studied. • The effects of interface inclination angle and load impact velocity were studied. • The strain field were analyzed based on the digital image correlation technique. • The variation of dissipated energy in the dynamic impact process was analyzed. The application of geopolymer has great potential in repairing damaged concrete. In engineering construction, the repaired structure is often affected by dynamic loading. Experimental research on the dynamic mechanical behavior and energy dissipation of geopolymer-concrete composites (GCC) is of great significance for understanding the bonding performance between geopolymer and concrete. In this paper, dynamic splitting experiment was performed on GCC under different interface inclination angles and load impact velocities by using the split Hopkinson pressure bar (SHPB). Then, the influence of interface inclination angle and load impact velocity on dynamic splitting tensile behavior and dissipated energy of GCC were discussed. Finally, the failure modes and strain field were analyzed based on digital image correlation (DIC) technique. The results indicate that the static peak load of GCC is roughly distributed around 26.0 kN and the dynamic peak load is 263.0 kN. The dynamic peak load measured by GCC is more than 10 times the static peak load. As the interface inclination angle increases from 0° to 90°, the dynamic peak load, static peak load and energy dissipation rate increase linearly, while the tensile sensitivity coefficient decreases. The energy dissipation ratio of GCC is kept between 0.30 and 0.40. In addition, the dynamic peak load, tensile sensitivity coefficient and dissipated energy increase gradually as the load impact velocity increases. A transition from interface failure to tensile failure can be found in GCC with the inclination angle increases. [ABSTRACT FROM AUTHOR]

• The undulation polypropylene fiber (UPF) performance and reinforcement effect in reducing crack development under freeze–thaw and dry–wet environments. • Freeze–thaw cycles cause significant damage to adhesion and friction, while dry–wet cycles mainly affect adhesion. • The interfacial strength is linear with the fiber curvature and the UCS of the substrate. The interfacial properties of fibers and matrix materials have an important effect on the mechanical properties of fiber-reinforced materials. To study the role of fiber morphology and the environmental effects on the interfacial properties of fibers and matrix materials, the interfacial strength characteristics of undulation polypropylene fiber (UPF) and serrated polypropylene fiber (SPF) with cement-modified iron tailings (CIT) were analyzed through single-fiber pullout tests. The effects of curing age, freeze–thaw cycles, and dry–wet cycles on interfacial strength were analyzed. The energy dissipation during fiber pullout under different environmental conditions was verified, and the microscopic mechanism of interfacial strength change was determined. The results show the following: (1) The interfacial strength of UPF and SPF is positively correlated with curing age, while freeze–thaw and dry–wet cycles can impair their interfacial properties; also, the interfacial strength decreases substantially and tends to flatten out after 3 cycles. (2) The dissipation energy of UPF and SPF increases with curing age, but decreases as the number of dry–wet cycles and freeze–thaw cycles increases. The critical reinforcement length of UPF is better than that of SPF by 363% and 50% under freeze–thaw and dry–wet cycles, respectively. Also, its performance and reinforcement effect in reducing crack development under freeze–thaw and dry–wet environments are better compared to SPF. (3) The interfacial strength of the profiled fibers consists of adhesion and friction. Freeze–thaw cycles cause a significant damage to adhesion and friction, while dry–wet cycles mainly affect adhesion. Interfacial strength is related to the curvature of the fiber and the unconfined compressive strength of CIT, which follows a linear function. [ABSTRACT FROM AUTHOR]

• Investigated the cyclic behavior of CSPSWs with two- and four-sided constraints. • Specimens were analyzed using a finite element model validated by experiments. • Seismic performance of CSPSW-2 and CSPSW-3 with two-sided constraints was similar. • Effect of initial damage on the seismic performance of CSPSWs was analyzed. Corrugated steel plate shear walls (CSPSWs) support vertical or horizontal corrugated plates attached to boundary frames through two- or four-sided connections. While two-sided constraints offer better applicability and convenience, this study aims to investigate the seismic behavior of CSPSWs with both two- and four-sided constraints. The investigation considers the coupling effects of direction, aspect ratio, thickness, and axial compression ratio. The study analyzes hysteresis curves, capacity characteristics, stiffness, ductility, and energy consumption for various failure modes. The results indicate that two-sided-constrained specimens exhibit lower mechanical properties compared to four-sided-constrained specimens, especially the initial stiffness. However, both constraint types show X-shaped tension fields diagonally along the CSP under low-cycle reciprocating loading. The horizontal and vertical directions of the corrugated plates have no significant impact on the seismic performance of the four-sided-constrained system, whereas they directly affect the stiffness and lateral load of the two-sided-constrained system. Additionally, an increase in plate thickness results in greater design requirements, particularly for surrounding frame members. Furthermore, when the axial compression ratio does not exceed 0.4, the specimen exhibits good seismic performance and energy dissipation capacity. [ABSTRACT FROM AUTHOR]

In the fracture analysis of materials or structures including cracks, defects and voids, the phase field method is one of the most efficient and popular methods. The phase field methods provide a stable and robust solution by regularizing the singularity of a mechanical system with discontinuities, and a regularization parameter is used for that. There is a powerful argument in the field of computational mechanics that regularization parameters should be regarded as material constants, and in many recently developed phase field models (PFMs), regularization parameters are used as material constants. In this paper, we derive a generalized form of a typical expression for the regularization parameter given as a material constant for making an in-depth analysis of the theoretical basis of such arguments, and estimate the rationality of this view through numerical analyses of some examples. • A generalized formula of the regularization parameter is derived. • The method for obtaining regularization parameters is given in three cases. • The models with the regularization parameters chosen from the formulas are checked. • The computational accuracy are evaluated based on the homogeneous solution. • The errors in the simulated maximum loads and crack paths are found. [ABSTRACT FROM AUTHOR]

Stilling basin is one of the dissipated energy structures in water transfer systems that its dimensions depend on the characteristics of hydraulic jump.In present study, six legs elements have been used in different permeability on basin bed and the changes of shear stress, sequent depth and the length of jump have been investigated. Experiments were conducted in a rectangular flume of 7.5 m long and 0.3 m wide and six legs elements were arranged on the bed of flume with density percent 36, 63 and 100 in such a way that the incoming water jet was just above the elements surface. The incoming Froude number was in the range of 5.3 to 8.1 and during each test the water surface profile and characteristics of hydraulic jump type A were measured. The results indicate that the most reduction of sequent depth ratio and dimensionless length of jump occur when the density of elements is 36%. In this study, relations have been presented for the sequent depth of hydraulic jump and shear force coefficient of bed as a function of the Froude Number for six legs elements.

The relative displacement of a piping system installed between isolated and nonisolated structures in a severe earthquake might be larger when without a seismic isolation system. As a result of the relative displacement, the seismic risks of some components in the building could increase. The possibility of an increase in seismic risks is especially high in the crossover piping system in the buildings. Previous studies found that an elbow which could be ruptured by low-cycle ratcheting fatigue is one of the weakest elements. Fatigue curves for elbows were suggested based on component tests. However, it is hard to find a quantitative evaluation of the ultimate state of piping elbows. Generally, the energy dissipation of a solid structure can be calculated from the relation between displacement and force. Therefore, in this study, the ultimate state of the pipe elbow, normally considered as failure of the pipe elbow, is defined as leakage under in-plane cyclic loading tests, and a failure estimation method is proposed using a damage index based on energy dissipation.

The double reduction method (DRM) is used to evaluate slope stability by weakening the two strength parameters in the Mohr–Coulomb criteria with two different reduction coefficients. The literature suggests various optimal reduction coefficient combinations (RCCs), but there is a lack of a suitable index to evaluate these combinations. The dissipated energy corresponds to the degree of material damage and the release of anti-sliding force of a slope. The higher the released anti-sliding force, the more serious the damage of the slope and the greater the associated dissipation of energy. Homogeneous slope examples show that different RCCs result in different dissipated energies when a slope becomes unstable. The dissipated energy can be used as an evaluation index to find the relative optimal RCC, which releases the greatest anti-sliding force of a slope from alternative RCCs. At the present stage, this method is limited only to homogeneous slope with two reduction coefficients. [ABSTRACT FROM AUTHOR]

Experimental and numerical studies investigating fatigue crack growth were conducted on flat samples made of stainless steel AISE 304 and titanium alloy Grade 2. The heat flux from the crack tip caused by plastic deformation localization was measured using the contact heat flux sensor previously developed by the authors. This provides a possibility to find a correlation between energy dissipation and crack propagation rate under fatigue uniaxial loading with constant stress intensity factor and under biaxial loading with constant stress amplitude. The experiments with constant stress intensity factor have shown a decrease in energy dissipation at constant crack rate and R=-1 (R=0). A theoretical analysis of the stress field at the fatigue crack tip has been carried out to explain this phenomenon. Based on the obtained results, the heat flux from the crack tip is represented as the sum of two functions describing energy dissipation in monotonic and reversible plastic zones separately. It has been shown that dissipation in a reversible plastic zone is a function of the applied stress amplitude only. This causes energy dissipation to decrease at constant stress intensity factor. The proposed phenomenology was successfully verified by testing both materials under biaxial loading.

The work is devoted to experimental study of heat flow evolution at the fatigue crack tip during biaxial loading. The plane samples of titanium alloy Graid-2 with thick of 1 mm were weakened by notch to initiate fatigue crack at the center of samples. Infrared thermography and the contact heat flux sensor based on the Seebeck effect are used to monitor the dissipated thermal energy. During tests the samples were subjected to cyclic loading of 10 Hz with constant stress amplitude and different biaxial coefficient. The experimental results confirm the previous conclusions of authors about two regime of energy dissipation at fatigue crack tip. The heat dissipation curve can be divided in two stages. Under the first stage the power of heat flux is proportional to the multiplication of the crack rate by its length. In the second stage is characterized by classical linear relationship between crack rate and heat flux rom the crack tip. The qualitative correspondence of the energy approach to the classical representation based on the stress intensity factor was shown.

A new yielding damper with pure torsional mechanism is introduced and investigated in this paper. Story shear force is transferred to the proposed device using special details to produce pure torsion without shear force and bending moment in the damper pipes. Hence, energy dissipation capacity of damper material could be efficiently used. Some relationships for structural characteristics of the proposed damper including initial stiffness, yielding and ultimate strength and load-displacement relation, are derived analytically. This is done by assuming a bi-linear curve for steel material considering its strain hardening. Ten specimens of this pure torsional damper were tested under cyclic loading. The hysteresis curves indicate a stable and well-shaped cyclic behavior. Results also show high energy absorption capacity and ductility for this damper. Widespread yielding and uniform stress distribution across the entire thickness of the pipe wall of the damper results in high equivalent viscous damping ratio from 38% to 48%. The structural characteristics of the tested specimens were compared with analytical relationships. In addition, a parametric study was conducted based on the analytical equations. • The hysteretic behavior of the proposed pure torsional damper (PTD) was stable in experimental tests. • PTD has high energy absorption capacity. • Analytical relationships obtained by considering bi-linear behavior for steel estimate experimental results accurately. • These relationships could be used with proper accuracy for designing PTDs. • Equivalent viscous damping ratio of 38–48% was observed for PTDs. [ABSTRACT FROM AUTHOR]

The influence of temperature on the fatigue properties of pseudoelastic NiTi under low-cycle fatigue are investigated. Tests were performed under the uniaxial tensile deformation (pull-pull) at 0°С and 20°С which is above the austenite finish temperature. Experimental results indicate that the fatigue life of NiTi alloy increases with the decrease of test temperature from 20°С to 0°С in the case of presenting the results depending on the strain range and dissipated energy. Regardless the test temperature, with the increase of number of cycles to failure, the stress and strain ranges, as well as the dissipation energy decrease, and the total dissipation energy and Odqvist’s parameter increase. The slope of the fatigue curves of NiTi alloy is greater at the temperature of 0°С in comparison with the 20°С in the case of employing the stress range, strain range, Odqvist’s parameter, and total dissipation energy as the failure criteria, and is less while employing the dissipation energy as the failure criterion [ABSTRACT FROM AUTHOR]

The article presents the results of experimental and finite element analyses of the flexural vibration behavior sandwich composite with different debonding ratios. Sandwich composite consists of two thin skins composed of E-glass fiber and epoxy resin bonded to lightweight and weaker core material of PVC foams. Experimental tests using the impulse technique were performed on the sandwich constituents and sandwich composites with different debonding lengths. The modal dynamic characteristics of sandwich composite were measured and discussed for each debonding ratio. A finite element modeling was used to determine the natural frequencies, modal shapes, and stress and strain fields for each element of sandwich composites for each debonding ratio. The modal strain energy approach was used to determine the contribution of energies dissipated of the core and the skins in the total dissipated energy and the global damping of the different sandwich composites. The results obtained by this approach are compared with those obtained experimentally. [ABSTRACT FROM AUTHOR]

Bearings acts as fusing components in bridges and transfer loads from superstructures to substructures. During earthquakes, bridge bearings may be subjected to large axial compressive loads and lateral displacements, and consequently experience severe damages. In this paper, an input energy-based (IEB) and a sliding displacement-based (SDB) damage index are proposed for quantifying seismic damage of the bridge bearings. The IEB damage index, previously proposed by authors, as the ratio of the dissipated energy to the earthquake input energy, and the SDB damage index is defined considering yielding displacement of the bearings corresponding to their sliding threshold. To evaluate the ability of the proposed damage indices in damage assessment of the bridge bearings, the force–displacement behavior of three commonly used bearings including elastomeric bearing, lead–rubber bearing, and flat sliding bearing are developed using rheological models. A set of the bearing specimens experimentally tested under cyclic/seismic loadings is adopted to calibrate the reliability of the damage indices. The results show that the IEB damage index provides a reasonably gradual progression of damage throughout the loading history and gives acceptable values for sliding and failure damage levels of the bearings more convincingly than the SDB damage model with respect to the experiment observations. [ABSTRACT FROM AUTHOR]

• Underground engineering instability is associated with rock damage evolution. • The progressive fracturing in intact and jointed marble is studied. • The irreversible strains and dissipated energy are computed as damage variables. • The influence of the intermediate principle stress and joint are quantified. Rock masses in underground engineering, such as mining and deep tunnelling engineering, are often repeatedly loaded and unloaded. Here, a series of true triaxial multi-level single cyclic loading tests (σ 1 > σ 2 > σ 3) were carried out on intact and jointed marble (50 × 50 × 100 mm3) to investigate the influence of the stress state and the absence or presence of a joint on the progressive damage process. The test results show that rock damage is directional and anisotropic. The irreversible strains in the σ 1 and σ 3 directions change linearly with cumulative damage, whereas the irreversible strains in the σ 2 direction decrease nonlinearly. The dissipated energy is appropriately linearly related to the equivalent irreversible strains. The damage variables based on the irreversible strains and dissipated energy are closely correlated, as determined by their similar fitted parameters. The stress state (σ 2 and σ 3), the absence or presence of a joint and the brittleness play a vital role in the rock damage evolution. More specifically, the parameter a has a logarithmic relationship with σ 3 and a linear relationship with σ 2. The relationship between the parameter a and the joint dip angle β can be fitted by a Gaussian distribution. In addition, the fitted parameter a decreases with increasing brittleness. [ABSTRACT FROM AUTHOR]

This study introduces U-shape metallic yielding damper (UMYD) as an energy dissipation system. This damper may be used as a replaceable and cost-effective tool and fuse in structural frames to improve lateral ductility, energy absorption and damping of structural systems under earthquakes. A series of static cyclic tests were conducted in order to examine the performance of UMYD and the response of force-displacement, lateral strength, elastic stiffness and energy absorption were achieved. Finite element numerical studies were conducted through changing damper geometrical parameters. Mathematical model was presented to estimate elastic stiffness of damper and was compared with numerical specimen results, which acceptable conformity. Finite elements models indicated that UMYD abilities energy absorbability in large displacements without loss of strength and stiffness, which may be a proper complementary system for lateral load-bearing systems. The behaviour of two 4- and 8-storey steel frames with moment resisting frame system was analysed under four different earthquakes under two states of with and without damper. The seismic performance of frames was analysed with respect to floors inter-storey drift, frame base shear and floors shear. The non-linear time historey analysis results demonstrated that 8-storey frame without UMYD failed to maintain the structure performance level within life-safety level, whilst under all states using damper, performance level remained within such level and a decrease in floors shear and inter-storey drift was observed. [ABSTRACT FROM AUTHOR]

To gain a further understanding of Freeze-Thaw weathering effect on the damage of sandstone from the perspective of energy analysis, uniaxial static compression tests were conducted on sandstone samples that suffered 0, 20, 60, 100 and 140 freezing-thawing cycles. Then total input strain energy, releasable elastic strain energy, dissipated energy and freezing-thawing induced damage of samples under uniaxial static compression tests were calculated and analyzed. In the mean time, the energy absorption of sandstone under dynamic loading tests (SHPB (Split-Hopkinson pressure bar) experiments) were cited and made a contrast with the dissipated energy of samples under uniaxial static compression tests. The results show that the tangent modulus, total input strain energy, releasable elastic strain energy and dissipated energy of samples decrease with Freezing-Thawing cycles go on, while the freezing-thawing induced damage grow with freezing-thawing cycles increase. In term of energy used for destroying rock samples in different test modes, less energy is needed for destroying samples in uniaxial static compression tests and it decreases with F-T cycles increase, while more energy is needed for destroying samples in dynamic impact loading and it increases with F-T cycles increase. In addition, the number of fragments of broken sample increase with the F-T cycles both in uniaxial static compression tests and dynamic loading tests, and sample under dynamic loading tests is more broken than sample under uniaxial static compression tests. [ABSTRACT FROM AUTHOR]

Experimental and numerical studies investigating fatigue crack growth were conducted on flat samples made of stainless steel AISE 304 and titanium alloy Grade 2. The heat flux from the crack tip caused by plastic deformation localization was measured using the contact heat flux sensor previously developed by the authors. This provides a possibility to find a correlation between energy dissipation and crack propagation rate under fatigue uniaxial loading with constant stress intensity factor and under biaxial loading with constant stress amplitude. The experiments with constant stress intensity factor have shown a decrease in energy dissipation at constant crack rate and stress ratio R=σmin/σmax=-1 (R=0). A theoretical analysis of the stress field at the fatigue crack tip has been carried out to explain this phenomenon. Based on the obtained results, the heat flux from the crack tip is represented as the sum of two functions describing energy dissipation in monotonic and reversible plastic zones separately. It has been shown that dissipation in a reversible plastic zone is a function of the applied stress amplitude only. This causes a decrease of energy dissipation at constant stress intensity factor. The proposed phenomenology was successfully verified by testing both materials under biaxial loading. [ABSTRACT FROM AUTHOR]

Lock-In thermography can be used to investigate elastic stresses and dissipative effects in dynamic processes like crack propagation. The evaluation normally is performed with a Discrete Fourier Transformation resulting in E- and D-Amplitude and phase images. The E-Amplitude images give information about the stress distribution, the D-Amplitude is connected with dissipated energies. The observed changes in the E-amplitude values can be attributed to a change in the stress state at the crack tip due to bending of the specimen caused by the propagating crack. In the crack propagation experiments the maximum value of the D-Mode in the area in front of the crack tip was found to be constant. The appearance of higher harmonic modes in the evaluation raises the question if the Discrete Fourier Transformation is the appropriate method for a quantitative evaluation of dissipative effects. Experiments performed on flat specimens show that the temperature change due to dissipative effects could not be described with a sine wave with the double loading frequency. Therefore, a quantitative determination of dissipated energies using the Discrete Fourier Transformation is impossible. For a quantitative determination of dissipated energies a new evaluation method has to be developed. [ABSTRACT FROM AUTHOR]

The work is devoted to experimental study of heat flux evolution at the fatigue crack tip during biaxial loading with a goal to relate the heat flux to the rate of crack propagation under different loading conditions. The plane samples of titanium alloy (Grade 2) 1 mm thick were weakened by notch to initiate fatigue crack at their centers. Infrared thermography and the contact heat flux sensor, which is based on the Seebeck effect, were used to monitor the dissipated thermal energy. The samples were subject to cyclic loading with constant stress amplitude at different biaxial coefficients. The experimental results confirmed the previous conclusions of the authors about two regime of energy dissipation at fatigue crack tip under Paris regime. At the first stage, the power of heat flux is proportional to the product of the crack rate by the crack length. The second stage is characterized by a traditional linear relationship between the crack rate and the heat flux. [ABSTRACT FROM AUTHOR]

During the last two decades, the semi-supported steel shear wall (SSSW) has been introduced as an alternative to the traditional form of steel plate shear wall (SPSW) system. In this paper, a numerical and experimental study on the behavior of a pinned connection steel frame with a mid-span shear panel, as well as the effect of opening existence on the system behavior is investigated. In this system, shear panel consisting of infill steel plate, stiffeners perpendicular to infill plate and secondary columns are placed in the middle of the steel frame span with pinned connections and unlike conventional SPSW system and SSSW system, the buckling of the infill plate is prevented and energy dissipation is carried out by shear. Experimental studies were performed on two specimens with a scale of 1:2. The characteristics of both specimens are the same and the only difference is the presence of opening in the second specimen. The results showed that in both specimens, the hysteretic curves were spindle-shape and without pinching. Moreover, numerical results were in good agreement with the experimental ones. Numerical studies showed that the energy dissipation and shear strength were increased with decreasing the opening ratio as well as decreasing height to thickness ratio of the infill plate. For example, in models with slenderness ratio of 200, the dissipated energy and maximum strength in the model with an opening ratio of 0.4 were about 47% and 38% less than that of the model without opening, respectively. [ABSTRACT FROM AUTHOR]

The results of the analysis of heat and stored energy variation in stainless steel AISI 304 under tension are presented in this work. The distributions of temperature and strain on the surface of specimens have been obtained by using infrared thermography and the digital image correlation of laser speckle patterns techniques. It has been found that the plastic flow diagram consists of two linear stages. The first one is characterized by the monotonic growth in evolved heat. At the second linear stage the portion of stored energy rises, that is connected with the growth in the rate of martensitic transformations. A temperature fluctuation in the center of a specimen at the true strain over 0.4 appears due to the motion of localized strain bands, which are also the sources of heat. [ABSTRACT FROM AUTHOR]

Highlights • The nonlinear behavior of fractured rock subject to cyclic loading has been presented. • A damage model for fractured rock is established. • This model takes into account the initial damage of rock and introduces the concept of equivalent modulus. Abstract In practical engineering, it is a common phenomenon of rocks subjected to cyclic loading. Such as mining engineering, subgrade engineering and earthquake engineering. In order to reveal the deformation properties of rock under cyclic loading and to establish the damage model, two groups of cyclic loading tests are carried out. Natural rocks show a remarkable nonlinear deformation property under the cyclic loading. The test results also reveal the evolutions of the elastic modulus and the residual strain of fractured rock. Energy dissipation is the essential characteristic of rock deformation and failure. Therefore, a damage model for fractured rock is established from the viewpoint of energy dissipation. This model takes into account the initial damage of fractured rocks and introduces the concept of equivalent modulus, which make the model more practical and easier to apply. [ABSTRACT FROM AUTHOR]

The traditional methodologies for fatigue life assessment of welded joints strongly depend on geometries and surface characteristics, as well as time. In this paper, an energy-based approach, independent of structures though thermal-graphic measurement, was presented to predict life expectancy of welded joints, via limited number of tests. In order to eliminate the thermal elastic effect caused by the welding residual stress, annealing was first conducted on welded specimens. Both monotonic and cyclic tests for welded joints were implemented. Then, based on the thermal evolution of welded joints measured by the quantitative thermo-graphic method, an energy-based approach, taking the linear temperature evolution and the intrinsic dissipation into account, was employed on the fatigue life prediction of flat butt-welded joints. The estimated results showed good agreement with the experimental ones, and the energy tolerance to failure E c for different stress amplitudes was found to be constant. [ABSTRACT FROM AUTHOR]

Bearing fatigue studies help to acknowledge many causes of the bearing failures. Nevertheless it is a necessity to analyze the individual bearing components in order to prevent exploitation breakdowns. The current paper aims to evaluate the total energy transfer of the bearing ball collisions that occur during the manufacturing processes. [ABSTRACT FROM AUTHOR]

Abstract GFRP rebars with different surface treatments such as helical wrapping and sand coating were evaluated under cyclic loads. The pull-out specimens were made from the addition of structural fibers (hooked end steel, PP, PVA fibers) with 1% of fiber volume fraction in a concrete matrix with expected change in interfacial bonding property as well as ductility improvement after first cracking. The experimental results were analyzed in terms of bond stress-slip curve, bond strength ratio, and energy dissipation. Severe failures in the interfacial layers of the GFRP rebars at the resin-bar fiber interface was observed as cycling loads increased. The addition of structural fibers to concrete generally showed significant changes for debonding failure mechanism since the strong bonding resulted in reduced energy dissipation as well as a sharp increase of load in the bond stress-slip curve. For the GFRP rebars, wedge effects from crushed or cracked particles due to repeated damage in the interfacial debonding zone affected the low dissipated energy. Abrupt pull-out bar failure was represented. The effect of fibers in the interfacial bonding layer confirmed that resistance of steel rebar to cycling debonding failures from rebar types showed the best performance. In particular, the addition of hooked steel fibers indicated the best performance regardless of rebar types. [ABSTRACT FROM AUTHOR]

The paper analyses the issue of functioning in the vicinity of the resonance of the mechanic equipment and/or devices with excitation sources the maximum perturbation force of which may be constant or variable related to the squared excitation pulsation. In both cases, the dynamic system does not remain constantly, stably and stationary on resonance point, the technological functionality being characteristic only for the ante/post-resonance regimens. For this reason, the proper notion of functioning in the vicinity of the resonance is used. There are dwelt with two distinct cases in this context, for a real dynamic model, from where it results the manner, we have to evaluate the maximal dissipated energy and maximal dissipated power related to the resonance regime. In both cases, the monotone increasing variation of the excitation pulsation requires contribution of energy from the source at the passage from ante-resonance to resonance or from resonance to post-resonance. [ABSTRACT FROM AUTHOR]

Highlights • A new stress sweep fatigue test for asphalt mixtures is proposed (called DUSST). • The new fatigue test is done in a shorter time than classical fatigue tests. • DUSST shows a good sensitivity of the main parameters evaluated. Abstract Fatigue cracking is one of the main damage mechanisms that take place in asphalt pavements. However, its evaluation during the design asphalt mixtures is not usually considered due to the complexity of the tests required, their high costs and the long time required to perform them. As a consequence, several research teams are working on developing new test procedures to reduce the time related to fatigue characterization of asphalt mixtures. In this context, this paper presents the development of a new test procedure consisting of a cyclic uniaxial tension-compression test in which the stress applied increases every 5000 cycles. In this manner, it is possible to evaluate a mixture's response under cyclic loading at different stress levels in one test. Also, failure of the mixture takes place in a shorter time period than that required by classical time sweep fatigue tests. This paper presents results obtained in the application of this new methodology to a mixture frequently used in Chilean pavement structures (type IV-A-12 by Chilean standards) with three different asphalt binders: a conventional binder (CA-24), a high modulus binder (CA-HM) and a polymer-modified binder (CA-PM). We evaluated three different types of aggregates obtained through two different shredding processes. Results achieved in the development of our Direct Uniaxial Stress Sweep Test (DUSST) show that it is an experimental method with great potential. This test can characterize fatigue behaviors of asphalt mixtures in a shorter time by using important parameters such as initial strain, failure strain, complex modulus and dissipated energy. In addition, we obtained a good sensitivity of the DUSST main parameters to variables evaluated. [ABSTRACT FROM AUTHOR]

Highlights • The aging process has a significant effect on fatigue life asphalt. • Warm mixtures containing sasobit had a higher fatigue life than hot mix. • Simple performance test failed to predict fatigue life of asphalt aging. • DE method, were able to characterize the fatigue behavior of mixtures aging. Abstract The aging process has a significant effect on the mechanical properties of asphalt mixtures, especially on fatigue parameter. Many approaches have been suggested to better understanding of the fatigue behavior of asphalt mixes. However, in many of these cases, the effects of aging are not considered. In this study, investigations were conducted to more accurately predict the fatigue life of asphalt mixes, independent of their ages. In this regard, the responses of the existing fatigue models in a wider range of asphalt mixtures were validated. For this purpose, hot and warm asphalt mixtures were used in both aged and unaged conditions. For the production of warm mixtures, Sasobit and RheoFalt were used as modifier additives. Indirect tension (IDT) test, resilient modulus and four-point bending fatigue beam test were performed separately WMA and HMA specimens. The results indicated that in all specimens, the aging of the asphalt mixture was always accompanied by increasing fracture energy and failure resistance. In addition, it was also found that those fatigue models that were based on simple performance tests failed to well predict the fatigue life of mixtures independently of the type of compounds, aging and loading conditions. Eventually, validations indicated that the behavior of dissipated energy during repeated loading to failure, have a significant role to precisely characterize the fatigue behavior independent of their age. [ABSTRACT FROM AUTHOR]

A numerical investigation regarding the seismic behavior of complex-3D steel buildings with perimeter moment resisting frames (PMRF) and interior gravity frames (GF) is conducted. The interior connections are assumed to be first perfectly pinned (PP) and then semi-rigid (SR); the two model responses are compared. Three steel building models representing low-, medium- and high-rise buildings, and several strong motions are used. The relative stiffness of SR connections is calculated according to the Richard Model and the Beam Line Theory. The Ruaumoko Computer Program is used to perform the required step-by-step nonlinear seismic analysis. Results indicate that interstory shears and interstory displacements at PMRF may be significantly reduced when interior connections are modeled as SR. Average reductions of up to 20, 46 and 11% are observed for interstory shears, for low-, medium-, and high-rise buildings, respectively. The corresponding reductions for interstory displacements are about 14, 44 and 15%. The contribution of GF to the lateral resistance is considerable, which significantly increases when the connections are modeled as SR; relative contributions larger than 80% are observed. The dissipated energy (DE) at PMRF is larger for the buildings with PP than for the buildings with SR connections indicating that damage at PMRF is reduced. Thus, the effect of the stiffness and the DE at interior connections should not be ignored. However, the design of some elements, particularly columns of the GF, has to be revised; these members may not be able to support the loads produced by the neglected lateral contribution if they are not properly designed. [ABSTRACT FROM AUTHOR]

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The corrugated steel plate shear walls have recently been proposed to address the seismic issues associated with simple steel plate shear walls; however, stiffness, strength, and ductility of the corrugated shear walls are significantly affected by varying the corrugation geometry under seismic loading. The present study investigates steel shear walls’ models with corrugated or simple infill plates subjected to monotonic and cyclic loads. The performance of the corrugated steel plate is evaluated and then compared to that of the simple steel plates by evaluating the damping ratios and energy dissipation capability. The effect of corrugation profile angle, the existence of an opening, and the corrugation subpanel length are numerically investigated after validation of the finite element modeling methodology. The results demonstrate that incorporating corrugated plates would lead to better seismic damping ratios, specifically in the case of opening existence inside of the infill plate. Specifically, the corrugation angle of 30° decreases the ultimate strength, while increasing the initial stiffness and ductility. In addition, the subpanel length of 100 mm is found to be able to improve the overall performance of shear wall by providing each subpanel appropriate support for the adjacent subpanel, leading to a sufficient buckling resistance performance. [ABSTRACT FROM AUTHOR]

• A novel fatigue crack growth method for shape memory alloys based on dissipated energy. • The method considers the intricate thermo-mechanical response of SMAs. • Powerful tool for crack propagation in SMAs based on force–displacement hysteresis data. A novel strain energy-based method for analyzing fatigue crack growth (FCG) in pseudoelastic Nickel-Titanium (NiTi) -based shape memory alloys (SMAs) is proposed. It uses the dissipated energy to predict the FCG. This parameter can be computed either by volume integration of near-crack-tip strain energy or by the force–displacement hysteresis measured at the loading pins of the sample. Eccentrically-loaded single Edge Crack tension samples (ESE(T)) were used for FCG tests. High resolution Digital Image Correlation (DIC) was used to capture near-crack-tip displacement and strain fields. DIC data were also used to estimate the effective stress intensity range by regressing the William's expansion series. Furthermore, a constitutive model for SMAs was used for FE simulations of ESE(T) samples, and the evolution of the dissipated energy during FCG tests was computed. Experimental FCG rate, plotted against the cyclic dissipated energy, are well fitted by a power law equation (R2 = 0.99). This result would open new perspectives to develop predictive models for FCG in SMAs considering intricate thermomechanical coupling mechanisms and material non-linearities. [ABSTRACT FROM AUTHOR]

• Mechanical response of CGBM under static-dynamic combined loads was studied. • Real-time monitoring of crack activities and strain field evolution was achieved. • Typical Failure modes of CGBM regarding various loading paths were identified. This study aims to investigate the mechanical properties and failure mechanisms for the cemented gangue backfill materials (CGBM) of the roadside filling structures along the gob-side entry with no coal pillars under static-dynamic combined loading. Cuboid cemented gangue backfill samples (CGBS) with dimensions of 50 × 50 × 100 mm were first prepared, with the fractal dimension D = 2.6 characterizing the particle size distribution of aggregates, and then conducted static-dynamic combined loading tests in terms of various pre-static loads (5–11 MPa), amplitudes (2–5 MPa), frequencies (1–16 Hz) and dynamic loading cycles (20–320 cycles). The test results indicate significant differences in the mechanical properties, acoustic emission (AE) responses, maximum principal strain fields, and ultimate failure modes of CGBS under different static-dynamic combined loading paths. With an increasing pre-static load, dynamic loading amplitude and number of cycles, the peak stress decreases by 21.28 %, 12.48 % and 11.84 % respectively, while the peak stress first decreases and then increases with the dynamic loading frequency and reaches the minimum value at the "characteristic frequency" of 4 Hz. The irreversible strain generally experiences an "acceleration - constant speed" variation during the dynamic loading as a result of the gradually stable damage effects. The dynamic elastic modulus increases by 45.84% in the pre-static load range of 5–11 MPa, while decreases with the dynamic loading amplitude. The dissipated energy increases by a factor of 6.5 with the dynamic loading amplitude, and by 27.52% with the pre-static loads. The significantly stimulated cracking activities at the beginning of dynamic loading result in extremely violent AE responses, and then the AE signals weaken due to the dominate role of opening and closure of existing cracks. The RA and AF calculation results illustrate that shear cracks become active at the initial dynamic loading and macroscopic failure stages. As the degradation effects of dynamic loading intensify, three various failure modes of inclined shear failure, "Y" shaped shear failure and conjugate shear failure for the CGBS are respectively classified, especially the conjugate shear failure characterized by two cone-shaped blocks. The findings will contribute to a better understanding of the mechanical responses and failure mechanisms of the roadside filling body during the dynamic mining. [ABSTRACT FROM AUTHOR]

• The S-N-R equation is proposed to fit the transverse fatigue life of GFRP lamina. • The relationship between UDE , stress level, stress ratio and fatigue cycles is built based on test results. • A cyclic creep strain model related to fatigue cycles, mean stress and stress amplitude is established. • The fracture surface is observed by SEM to reveal the fatigue damage mechanism. Inadequate transverse or shear strength is the key factor contributing to the failure of pultruded GFRP structures. In this paper, the static and fatigue performance of 90° pultruded unidirectional GFRP lamina were tested. A series of macroscopic phenomenological models were established to describe the performance variations during cyclic loading, including fatigue life, energy dissipation capacity and cyclic creep strain. The fracture surfaces of specimens were observed by a field-emission scanning electron microscopy (SEM). Experimental results indicated that the transverse fatigue life of GFRP unidirectional lamina can be fitted by S - N - R regression equation. The transverse stiffness degradation can be even ignored during fatigue loading. The results also show that the proposed equations can reasonably reflect the growth trend of dissipated energy per unit volume (UDE) and successfully predict cyclic creep strain increment of pultruded GFRP during cyclic loading. [ABSTRACT FROM AUTHOR]

This work is devoted to the development of an experimental method for studying the energy balance during cyclic deformation and fracture. The studies were conducted on 304 stainless steel AISE and titanium alloy OT4-0 samples. The investigation of the fatigue crack propagation was carried out on flat samples with different geometries and types of stress concentrators. The heat flux sensor was developed based on the Seebeck effect. This sensor was used for measuring the heat dissipation power in the examined samples during the fatigue tests. The measurements showed that the rate of fatigue crack growth depends on the heat flux at the crack tip.

The technique of rapid evaluation of fatigue limit using infrared thermography has been paid attention during the past 30 years. This technique is beneficial because it also makes possible to detect the location of fatigue damage in real structures. In this technique, the second harmonic of temperature variation during cyclic loading is often used as a measure of the temperature evolution to evaluate the fatigue limit. The source of the second harmonic has been already investigated quantitatively for the load amplitude above the fatigue limit but has not been investigated very well for the load amplitude below the fatigue limit. In this research, five factors (second harmonic caused by energy dissipation, applied load signal, photoelectric current of infrared sensor, quantization error and specimen movement) were examined quantitatively to examine the source of the second harmonic below the fatigue limit. Experiments were conducted for double edge notched specimens of type 304 stainless steel. As a result, it was found that the second harmonic of temperature variation below the fatigue limit is mainly caused by loading equipment. In conclusion, it is suggested that the fatigue limit should be evaluated by fitting curves considering the second harmonic proportional to the square of the load amplitude.

In an attempt to find possible solution for avoiding premature occurrences of brittle fracture in rectangular hollow section (RHS) column-to-I beam connections, an improved type of connection was tested by authors. Instead of welding, the beam was connected to the flange plates by bolts, some distance away from the column face. A series of test was conducted on this improved RHS column-to-I beam flange-plate bolted connection, the results show that the improved connection does not fail by fracture as observed in the conventional connections and has a larger energy dissipation capacity. This paper describes the finite element modeling method employed to analyses both conventional welded RHS column-to-I beam and improved bolted connections. Three highly complex 3D finite element models are created, accounting for material nonlinearity, large deformation and contact behavior involved in the models. The connection models have been analyzed under some loading conditions up to failure. The comparisons with experimental data show that the finite element models have high level of accuracy and can be employed to further optimize the connection design. In addition, the ultimate moment capacity of this improved connection is found to be predicted by simple formulas based on an elementary plastic analysis, and the connection has sufficient overstrength to allow formation of plastic hinges at the beam ends.

The article presents results of experimental tests of energy parameters of hard coals under loading, collected from research sites located within five main geologic structures of Upper Silesian Coal Basin (GZW) - Main Trough, Main Anticline, Bytom Trough, Rybnik Trough and Chwałowice Trough. Coals from12 mines were analysed, starting with seams of group 200, through groups 400, 500, 600 and, finally, seams of group 700. Coal of each of the groups of seams underwent uniaxial compression stress of the energy parameters, in a servo-controlled testing machine MTS-810NEW, for the full range of strain of the tested coal samples. Based on the tests the dependence of different types of specific energy of longitudinal strain of coals on the value of uniaxial compression strength was determined. The dependence of the value of dissipated energy and kinetic energy of coals on the uniaxial compression strength was described with a linear function, both for coals which due to their age belong to various bed sand for various lithotypes of coal. An increase in the value of dissipated energy and in kinetic energy was observed, which was correlated with an increase in uniaxial compression strength of coal. The share of dissipated energy is dominant in the total energy of strain. Share of recoverable energy in the total energy of strain is small, independent of the compression strength of coals and is at most a few per cent high. In coals of low strength and dominant share of dissipated energy, share of recoverable energy is the biggest among the tested coals. It was shown that following an increase in compression strength the share of recoverable energy decreases, while the share of dissipated energy in the total energy increases. Further studies of specific energy of longitudinal strain of rocks in the full-range strain will be the next step inperfecting methodology of research into natural rock burst susceptibility of Carboniferous rock mass and changes in the susceptibility resulting from mining activity.

Surrounding rock deformation and consequent support failure are the most prominent issues in red-bed rock tunnel engineering and are mainly caused by the effects of unloading, rheology, and swelling. This study investigated the mechanical responses of two kinds of red-bed mudstone and sandstone under unloading conditions via laboratory observation. Volume dilation was observed on the rocks during unloading, and the dilatancy stress was linear with the initial confining pressure. However, the ratios of dilatancy stress to peak stress of the two rocks kept at a range from 0.8 to 0.9, regardless of confining pressures. Both the elastic strain energy and the dissipated energy evolved synchronously with the stress-strain curve and exhibited conspicuous confining pressure dependence. Special attention was paid to the evolution behavior of the dilatancy angle. The dilatancy angle changed linearly during unloading. When the confining pressure was 10 MPa, the dilatancy angle of mudstone decreased from 26.8° to 12.5° whereas the dilatancy angle of sandstone increased from 34.6° to 51.1°; when the confining pressure rose to 25 MPa, the dilatancy angle of mudstone and sandstone decreased from 45.8° to 17.4° and increased from 21.7° to 39.5°, respectively. To further understand the evolution of the dilatancy angle, we discussed the links between the variable dilatancy angle and the processes of rock deformation and energy dissipation.